In the operation of fluid actuated work elements, for example left and right tracks of a crawler type tractor, it is desirable to provide means for selectively, controllably delivering hydraulic fluid to the track motors at substantially common rates. If the fluid delivery rate changes, one track will move faster than the other track, which will cause the vehicle to undesirably turn. This is particularly pronounced where the load changes on one of the tracks as, for example, when one of the tracks is scrubbing against an embankment or a large rock. Such control is also more difficult where each track is served by a separate hydraulic fluid pump.
This invention therefore resides in apparatus for selectively, controllably delivering fluid from separate variable displacement pumps in response to a load pressure signal acting on a single pump control valve serving said pumps.